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Hilcorp Natural Gas Leak From 8-Inch Pipeline

Cook Inlet between Platform A and Nikiski. (Lat/Long: 60.776367, -151.43365)
Spill Id
Product/ Quantity
The natural gas being released is not natural gas from the platform. The gas is processed dry natural gas (98.67% Methane), providing fuel gas to four platforms: Platform A, Platform C, Dillon Platform and Bakers Platform. The exact amount of gas released to water is unknown at this time. Following the placement of temporary clamp on the line, the pressure has stabilized at 66 psi.
Hilcorp was unable to determine the cause of the spill until recently when ice conditions allowed divers to access the site. A large rock, approximately 3 feet by 10 feet, was identified as causing a breech on the line that is 3/16 inch wide by 3/8 inch long.

ADEC Situation Reports


May 20 Line pressure tested to 550 psi. No bubbles or leaks were observed.
May 19 Hilcorp complete permanent clamp installation
May 13 Hilcorp remobilized the dive team to install the permanent clamp
May 10 PHMSA approved the permanent repair plan
May 10 Hilcorp submitted Environmental Sampling and Monitoring Report for sampling period #8 ending May 9.
May 3 Hilcorp submitted Environmental Sampling and Monitoring Report for sampling period #7 ending May 2.
May 1 PHMSA’s deadline for Hilcorp to stop the leak.
April 26 Hilcorp submits Environmental Sampling and Monitoring Report for sampling period #6 ending April 25.
April 24 Hilcorp demobilized divers from the site to await PHMSA’s approval of a permanent repair plan.
April 22 Dive crew locates a flat spot on the pipe from the 3 o’clock to 6 o’clock position due to wear from a rock. Measurement shows the pipe is 1/8” out of round at that location.
April 21 Dive crew was able to get the temporary repair clamp properly torqued to seal properly, stopping the leak.
April 20 Dive crews remove permanent clamp because they are unable to get it to seal properly. They reinstall the temporary clamp, but run out of time to get the bolts sufficiently torqued to completely stop the leak. 
April 20 5th Agency wildlife monitoring flight. Plentiful bird activity (roughly 2,000 birds noted). Extremely little ice. Seven beluga whales spotted near mouth of Beluga River.
April 19 Hilcorp reduces line pressure to 52 psi. Dive crews remove the temporary repair clamp and install the permanent repair clamp but unable to get it to seal properly.
April 19 Hilcorp submits Environmental Sampling and Monitoring Report for sampling period #5 ending April 18.
April 18 Dive crew continues preparation of pipeline leak location for installation of permanent repair clamp.
April 17 ADEC publishes SITREP#5. Dive crew continues preparation of pipeline for permanent repair clamp.
April 14 - 16 Dive crew prepares the pipeline for installation of a permanent repair clamp.
April 13 Divers successfully installed the temporary repair clamp on the evening of April 13 and stopped the leak.
April 12 Hilcorp submits Environmental Sampling and Monitoring Plan Summary Report for sampling period #4 ending on April 11, 2017.
April 12 PHMSA issues a Consent Agreement between PHMSA and Hilcorp regarding the Middle Ground Shoal Fuel Gas Pipeline “A”. This agreement replaces the Notice of Proposed Safety Order (NOPSO) issued to Hilcorp on March 3, 2017. This Consent Agreement includes the following topics:
  • Repair of the pipeline
  • Notification of pressure fluctuations
  • Temporary pressure restriction
  • Leak Inspection and Repair Plan
  • Shutdown Plan
  • Environmental Sampling and Monitoring Obligations
  • Modification and Inspection Plan
April 12 Three additional dives were conducted to further stabilize the pipeline; prep the surface to install the temporary clamp; and install a temporary clamp near the 3/8” x 3/16” hole.
April 11 Three dives were conducted to clean the pipeline exterior with a wire brush to ensure proper sealing between the repair clamp and pipeline; place pipeline supports on the seafloor; lift the pipeline approximately 16 inches above the rocky substrate; and install supports to temporarily secure the pipeline from movement.
April 8 Hilcorp reduced the line pressure to 59 psi, reportedly reducing the line leak rate to 78,000 to 108,000 cubic feet per day.
April 8 Hilcorp’s diving contractor successfully completed two dives. Divers reported a 1-1” long transverse abrasion to the line in the six o’clock position that appeared to have been caused by abrasion against a 3’ x 10’ rock imbedded in the sea floor approximately 2”from the pipe. Divers attempted to initiate temporary repair. Initial repair efforts were hampered due to insufficient clearance between the leaking pipe and the boulder and short operating windows during slack tide.
April 6 A fourth state agency wildlife observation overflight was provided by Hilcorp.
April 5 Hilcorp submits Environmental Sampling and Monitoring Plan Summary Report for sampling period #3 ending on April 4, 2017.
March 29 Hilcorp submits Environmental Sampling and Monitoring Plan Summary Report for sampling period #2 ending on March 28, 2017.
March 25 Hilcorp reduced the line pressure down to 65 psi, reportedly reducing the line leak rate to 85,000 to 115,000 cubic feet per day.
March 23 ADEC provides response to Hilcorp’s Environmental Sampling and Monitoring Plan Summary Report for sampling period #1 with initial comments from review. ADEC continues to review the report more fully.
March 22 Hilcorp submits Environmental Sampling and Monitoring Plan Summary Report for sampling period #1 ending on March 21, 2017.
March 14 ADEC publishes SITREP#4.
March 14 ADEC issues letter detailing preliminary initial approval of Hilcorp to commence the sampling and monitoring plan as described.
March 8 Hilcorp submits environmental sampling and monitoring plan to ADEC. Hilcorp also submits letter regarding the pipeline shutdown contingency plan which details Hilcorp’s intent to submit the pipeline shutdown plan to PHMSA, as required by PHMSA’s Notice of Proposed Safety Order.
March 3 PHMSA issues Notice of Proposed Safety Order.
March 1 ADEC publishes SITREP#3.
February 27 Center for Biological Diversity issues Notice of Intent to Sue.
February 27 ADEC sends letter to Hilcorp, again asking for a sampling and monitoring plan to be submitted by March 8 in order to determine environmental impacts. ADEC also requests pipeline shutdown plans to be submitted by March 13.
February 24 ADEC issues a Notice of Violation to Hilcorp, stating the company is releasing a hazardous substance and needs to control it.
February 21 ADEC publishes SITREP#2.
February 20 Hilcorp responds to ADEC’s February 10 letter, stating the spill is not unduly harming the environment and the company will not be able to safely stop the leak until the ice conditions improve. Hilcorp’s written response does not adequately address monitoring plans, as requested.
February 15 ADEC publishes SITREP#1.
February 15 Citizen-based non-profit organization, Cook Inletkeeper, sends Notice of Intent to Sue Hilcorp under the Clean Water Act.
February 14 ADEC requests Hilcorp conduct overflights of leak site.
February 10 ADEC sends Letter of State Interest requesting information about stopping the leak and plans for monitoring and mitigation in the interim until pipeline repaired.
February 9 ADEC informs Hilcorp of jurisdiction over the discharge of any hazardous substance in Alaska.
February 7 Cook Inlet Regional Citizens Advisory Council engaged.
February 7 Leak reported by Hilcorp; USCG, NRC, ADEC, PHMSA notified.
Incident Location

Contact Information

Hilcorp Sampling and Monitoring Results

  • Posting Hilcorp’s reports summarizing sampling results on the Department’s incident webpage does not indicate concurrence with the results or their conclusions. The reports are being made available to the public in the spirit of transparency. The Department’s review of submitted results is ongoing.

State Agency Wildlife Overflights

Other Documents


  • ADEC SOSC: Geoff Merrell, 907-267-7682
  • ADEC PIO: Candice Bressler, 907-465-5009
  • PHMSA: Dave Mulligan, 720-963-3193
  • HILCORP ALASKA: Lori Nelson, 907-777-8300
  • NOAA FISHERIES: Julie Speegle, 907-586-7032
  • ADF&G: Jeanette Alas, 907-267-2805

Notice to Mariners

  • The U.S. Coast Guard has released the following notice to mariners on February 16, 2017: Due to the current level of ice in lower Cook Inlet, natural gas may be accumulating under the ice and unable to be dissipate safely into the atmosphere. Mariners are requested to stay outside of a 1,000-yard radius of the location and transit the area with caution.

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